feat(scan): weak-crypto rules for Python — coverage 65.9% → 71.3% (v0.9.0) - #102
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…e seed)
Raises detection coverage against the testbed from 65.9% to 71.3% (85 to 92 of
129), false-positive rate still 0%. The CWE-327/338 cluster was the largest
recoverable gap: primitives threatcrush had generic rules for, but scoped to a
credential on the matched line, so Python's integrity- and confidentiality-use
cases slipped through.
Three Python rules, each keyed on a signal that survives without trusting a
name:
- py-broken-cipher: DES/RC2/RC4/Blowfish construction, and AES in ECB mode.
No safe use, so inherent — flagged wherever it appears. AES matches only on
ECB, leaving GCM/CTR/CBC alone.
- py-weak-hash: hashlib.md5/sha1, unless the line carries Python's own
`usedforsecurity=False` opt-out for a non-security digest.
- py-predictable-random-seed: random.seed() from the clock or pid, which
makes the whole sequence reproducible. A fixed integer seed (reproducible
tests) is left alone.
What is deliberately NOT added: a rule for a `random`-drawn token whose only
signal is the enclosing function name (`generate_session_id`). Guard windows
exclude definition lines on purpose — a name is not evidence, the same reason a
`def sanitize_…` does not count as sanitisation — so there is no line-level
signal to key on. The generic `insecure-randomness-for-secret` still catches
the common `token = …random…` shape. Those name-only cases are the documented
tail, pinned by a test that asserts they stay silent.
The coverage gate floor moves 60 to 68 to lock the gain in; a regression below
the new baseline now fails the job. No new findings on capacitor (10,
unchanged) or the self-scan (67, unchanged) — the rules are Python-only and
precise. 141 tests, up from 134.
Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>
ThreatCrush Security Scan67 finding(s) HIGH/CRITICAL: 11 | MEDIUM: 55 | LOW: 1
…and 17 more. Full results in the Security tab. Snippets are redacted; ThreatCrush never prints matched credential material. |
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Release 0.9.0. Raises detection coverage against the testbed from 65.9% → 71.3% (85 → 92 of 129), false-positive rate still 0%.
The gap
The CWE-327/338 cluster was the largest recoverable miss — primitives threatcrush had generic rules for (
weak-hash-on-credential,insecure-randomness-for-secret), but scoped to a credential on the matched line. Python's integrity- and confidentiality-use cases carry the security role in the enclosing function, not on the line, so they slipped through.Three Python rules
Each keyed on a signal that survives without trusting a name:
py-broken-cipherDES/RC2/RC4/Blowfish.new(...),AES.new(..., MODE_ECB)inherent; AES matches only on ECB, GCM/CTR/CBC left alonepy-weak-hashhashlib.md5/sha1(...)usedforsecurity=Falsepy-predictable-random-seedrandom.seed(<clock/pid>)What I deliberately did not add
A rule for a
random-drawn token whose only signal is the enclosing function name (generate_session_id,generate_mfa_code). Guard windows exclude definition lines on purpose — a name is not evidence, the same reason adef sanitize_…doesn't count as sanitisation. There's no line-level signal left to key on, so forcing it would mean either trusting names (a documented regression risk) or shape-heuristics that add false positives for marginal gain.The generic
insecure-randomness-for-secretstill catches the common real shape (token = "".join(random.choice(...))). The name-only cases are the documented tail, pinned by a test asserting they stay silent. Honest boundary, not an oversight.Verification
tsc --noEmitclean.The debugging that shaped this is worth a line: my first attempt keyed the PRNG rule on a credential term in the enclosing
def, and it only "worked" on one line — by a fluke, its trailing comment contained "MFA". Tracing that is what surfaced the deliberate definition-line exclusion, and turned a rule that passed by accident into a boundary I can defend.